U.S. patent number 5,310,848 [Application Number 08/010,763] was granted by the patent office on 1994-05-10 for resin composition for powder coating.
This patent grant is currently assigned to Nippon Ester Co., Ltd.. Invention is credited to Katsuyoshi Atsumi, Tokuzo Nozaki, Makiko Sakai.
United States Patent |
5,310,848 |
Nozaki , et al. |
May 10, 1994 |
Resin composition for powder coating
Abstract
a resin composition for a powder coating comprising a polyester
A, which does not substantially set to gel and has a hydroxyl value
of at least 1,200 g eq/10.sup.6 g, a polyester B, which does not
substantially set to gel and has a hydroxyl value of from 200 to
1,000 g eq/10.sup.6 g, and an inner blocked isocyanate hardener,
wherein the weight ratio of polyester A to polyester B is from
70:30 to 10:90 and the difference (absolute value) in gel time
between these polyesters A and B is at least 3 minutes.
Inventors: |
Nozaki; Tokuzo (Aichi,
JP), Atsumi; Katsuyoshi (Aichi, JP), Sakai;
Makiko (Aichi, JP) |
Assignee: |
Nippon Ester Co., Ltd. (Aichi,
JP)
|
Family
ID: |
12528459 |
Appl.
No.: |
08/010,763 |
Filed: |
January 29, 1993 |
Foreign Application Priority Data
|
|
|
|
|
Jan 29, 1992 [JP] |
|
|
4-038552 |
|
Current U.S.
Class: |
528/45; 524/196;
528/80; 528/83; 528/283; 525/445; 525/187; 524/534; 525/440.02 |
Current CPC
Class: |
C08G
18/798 (20130101); C09D 167/00 (20130101); C08G
18/4202 (20130101); C09D 167/00 (20130101); C08L
67/00 (20130101); C08L 2666/28 (20130101); C08G
2150/20 (20130101) |
Current International
Class: |
C08G
18/00 (20060101); C08G 18/79 (20060101); C08G
18/42 (20060101); C09D 167/00 (20060101); C08G
018/30 (); C08G 018/80 () |
Field of
Search: |
;524/539,196
;528/45,80,83 ;525/440 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
Other References
IPDI-BF 1540, "Cross-Linking agent free from blocking agent for
saturated polyesters containing OH groups", published by Huls
Company..
|
Primary Examiner: Michl; Paul R.
Assistant Examiner: Asinovsky; Olga
Attorney, Agent or Firm: Sughrue, Mion, Zinn, Macpeak &
Seas
Claims
What is claimed is:
1. A resin composition for a powder coating comprising a polyester
A which does not substantially set to gel and has a hydroxyl value
of at least 1,200 g eq/10.sup.6 g, a polyester B which does not
substantially set to gel and has a hydroxyl value of from 200 to
1,000 g eq/10.sup.6 g, and an inner blocked isocyanate hardener,
containing, self-blocked isocyanate groups of the formula: ##STR2##
wherein the weight ratio of said polyester A to said polyester B is
70:30 to 10:90 and the difference (absolute value) in gel time
between said polyester A and said polyester B is at least 3
minutes.
2. A resin composition for a powder coating as in claim 1, wherein
said polyester A is a polyester comprising terephthalic acid and/or
isophthalic acid with trimethylolpropane and said polyester B is a
polyester comprising terephthalic acid and/or isophthalic acid with
ethylene glycol and/or neopentyl glycol.
3. A resin composition for a powder coating as in claim 1, wherein
the difference (absolute value) in acid value between said
polyester A and said polyester B is at least 20 g eq/10.sup.6
g.
4. A resin composition for a powder coating as in claim 1, wherein
the hydroxy value of said polyester A is from 2,000 to 5,000 g
eq/10.sup.6 g.
5. A resin composition for a powder coating as in claim 1, wherein
the difference (absolute value) in gel time between said polyester
A and said polyester B is from 5 to 15 minutes.
6. A resin composition for a powder coating as in claim 1, wherein
the softening points of said polyester A and said polyester B are
from 50 to 150.degree. C.
Description
FIELD OF THE INVENTION
The present invention relates to a resin composition for a powder
coating capable of giving a mat or semimat coating film.
BACKGROUND OF THE INVENTION
Common examples of powder coatings include epoxy-series,
acryl-series and polyester-series. It is well known that
polyester-series powder coatings have well-balanced coating
performance.
Powder coatings have been widely used in various fields including
appliance, automobile and construction materials. In some cases, a
glossy coated surface (specular gloss at 60.degree.: approximately
90 to 100%) is required for aesthetic purposes, while a mat
(specular gloss at 60.degree.: approximately less than 30%) or
semimat (specular gloss at 60.degree.: approximately 30 to 70%) may
be required for other purposes.
Examples of conventional methods for preparing a powder coating
capable of giving such a mat or semimat coating film include a
method comprising adding a large amount of a pigment of coarse
particles, and another method comprising dry-blending a
polyester-series powder coating with an acryl-series powder
coating.
However, the addition of a large amount of a pigment of coarse
particles causes a deterioration in smoothness or a decrease in
mechanical strength of the coating film. On the other hand, when
using the method of dry-blending the two powder coatings, a mat or
semimat powder coating cannot be obtained by a single step, which
increases production cost. Furthermore, this method suffers from
other problems including heterogeneity of the resulting blend and a
change in the blending ratio during recovery and application.
In order to solve the above-mentioned problems, JP-A-64-1770 (the
term "JP-A" as used herein means an "unexamined published Japanese
patent application") proposes a resin composition for a powder
coating comprising a polyester having a hydroxyl value of at least
1,200 g eq/10.sup.6 g, another polyester having a hydroxyl value of
from 200 to 1,000 g eq/10.sup.6 g and a blocked isocyanate hardener
wherein the difference in gel time between the two polyesters is at
least 3 minutes.
In the case of a powder coating comprising this resin composition
for a powder coating, however, a large amount of a di- or
tri-functional blocked isocyanate hardener should be blended in
order to control the functional value to a level almost equivalent
with the hydroxyl value, since a polyester having a hydroxyl value
of at least 1,200 g eq/10.sup.6 g is contained therein. As a
result, there occur some troubles, for example, contamination of a
stove or a material to be coated due to vaporization of a large
amount of a blocking agent during the reaction between the
polyester and the blocked isocyanate hardener and a weight loss of
10% or above.
SUMMARY OF THE INVENTION
An object of the present invention is to solve the above-mentioned
problems by providing a resin composition for a powder coating
whereby a stable mat or semimat coating film can be obtained
without causing a trouble of the contamination of a stove or a
material to be coated and with a small weight loss during the
reaction.
As a result of extensive studies, the present inventors have found
that the above-mentioned object can be achieved by combining two
types of polyesters each having a specific hydroxyl value with an
inner blocked isocyanate hardener accompanied by no vaporization of
a blocking agent during the hardening reaction, thus completing the
present invention.
Accordingly, the present invention provides a resin composition for
a powder coating comprising a polyester A, which does not
substantially set to gel and has a hydroxyl value of at least 1,200
g eq/10.sup.6 g, a polyester B, which does not substantially set to
gel and has a hydroxyl value of from 200 to 1,000 g eq/10.sup.6 g,
and an inner blocked isocyanate hardener, wherein the composition
ratio (by weight) of polyester A to polyester B is from 70:30 to
10:90 and the difference (absolute value) in gel time between
polyester A and polyester B is at least 3 minutes.
DETAILED DESCRIPTION OF THE INVENTION
In the present invention, a hydroxyl value and a gel time are each
a value determined by the method as specified below.
Hydroxyl Value
Determined by acetylating a polyester sample and then titrating
with a solution of potassium hydroxide in methanol.
Gel Time
To a polyester sample, there are added an inner blocked isocyanate
hardener (IPDI-BF 1540, manufactured by Huls Co.), in such an
amount that functional groups become equivalent, and 33% by weight
of a titanium dioxide powder. Then the hardening curve of 90 g of
the obtained sample is formed by using a Brabender Plasti-Corder
(manufactured by Brabender Co.) at a temperature of 200.degree. C.
The time to inflection point is referred to herein as the "gel
time".
In the present invention, the expression "inner blocked isocyanate"
means a compound which has the following bond consisting of
self-blocked isocyanate groups but does not have the group which
functions as an isocyanate group other than the self-blocked
isocyanate groups: ##STR1##
In the resin composition of the present invention, the hydroxyl
value of polyester A should be at least 1,200 g eq/10.sup.6 g,
preferably from 2,000 to 5,000 g eq/10.sup.6 g, while that of
polyester B should be from 200 to 1,000 g eq/10.sup.6 g. When the
hydroxyl value of polyester A is less than 1,200 g eq/10.sup.6 g, a
good matting effect cannot be achieved. When the hydroxyl value of
polyester B is less than 200 g eq/10.sup.6 g, the surface of the
coating film suffers from significant unevenness, and therefore the
smoothness thereof is deteriorated. When the hydroxyl value of
polyester B exceeds 1,000 g eq/10.sup.6 g, on the other hand, the
mechanical strength of the coating film is deteriorated or only a
poor matting effect is achieved.
It is required that both of polyesters A and B are polyesters which
do not substantially set to gel. The expression "polyester which
does not substantially set to gel" as used herein means a polyester
which can be ground with the use of a common mill and is flowable
when melted. When a polyester has set to gel, it is difficult to
formulate the resin composition into a coating and, furthermore,
the obtained coating film fails to give an even surface.
In the present invention, an inner blocked isocyanate hardener is
to be used as a hardener. The inner blocked isocyanate hardener, in
which isocyanate groups have been self-blocked, contains no
blocking agent. Therefore, it never suffers from any troubles such
as the contamination of a stove or weight loss due to the
vaporization of a blocking agent during the hardening reaction. As
an example of such a hardener, uretdione-bound self-blocked
isophorone diisocyanate, which is marketed from Huls Co. under a
tradename "IPDI-BF 1540", may be cited.
It is preferable to use the hardener in such an amount that
equivalency of the number of its functional groups to the number of
hydroxy groups in the polyester resins is from 0.8 to 1.2.
In the resin composition of the present invention, the composition
ratio (by weight) of polyester A to polyester B is from 70:30 to
10:90, preferably from 40:60 to 20:80. When the composition ratio
does not fall within the broader range, a satisfactory matting
effect cannot be achieved.
In the resin composition of the present invention, the difference
(absolute value) in gel time between polyesters A and B should be
at least 3 minutes. When said difference in gel time is shorter
than 3 minutes, a sufficient matting effect cannot be achieved. In
order to obtain a highly mat coated film (specular gloss at
60.degree.: less than 20%), it is preferable that said difference
is from 5 to 15 minutes. When the difference in gel time of
polyester resins to be used does not fall within this range, only
an unsatisfactory matting effect is achieved or the mechanical
strength of the coating film is deteriorated.
In the present invention, the degree of matting can be controlled
by adjusting the hydroxyl value of polyester A, the weight ratio of
polyesters A and B, and the difference in gel time between these
polyesters. When the hydroxyl value of polyester A is approximately
3,000 g eq/10.sup.6 g or above and the weight ratio of polyester A
to polyester B is 30:70, for example, a completely mat coated face
(specular gloss at 60.degree.: less than 10%), a mat coated face
(specular gloss at 60.degree.: approximately 20%) and a semimat
coated face (specular gloss at 60.degree.: 50 to 60%) can be
obtained by adjusting the difference in gel time between these
polyesters to at least 6 minutes, approximately 5 minutes and
approximately 3 to 4 minutes, respectively.
In the resin composition of the present invention, it is preferable
to control the difference (absolute value) in acid value between
polyesters A and B to at least 20 g eq/10.sup.6 g. When the
difference in acid value between these polyesters is excessively
small, the specular gloss at 60.degree. of a coated face varies
within a range of from several percent to 50% especially when a
completely mat coated surface of a specular gloss at 60.degree. of
10% or less is to be formed, and, therefore, a mat coated face
having a stable specular gloss cannot be obtained.
As polyester A, those obtained from the following carboxylic acid
components and alcohol components may be preferably employed.
Carboxylic Acid Component
Materials comprising terephthalic acid and/or isophthalic acid
optionally together with other polyvalent carboxylic acids such as
aromatic dicarboxylic acids (for example,
2,6-naphthalenedicarboxylic acid), aliphatic dicarboxylic acids
(for example, succinic acid, adipic acid, azelaic acid), alicyclic
dicarboxylic acids (for example, 1,4-cyclohexanedicarboxylic acid)
and a small amount of tri- or higher valent carboxylic acids (for
example, trimellitic acid, pyromellitic acid).
Alcohol Component
Materials comprising trifunctional alcohols such as
trimethylolethane, trimethylolpropane, 3-methylpentane-1,3,5-triol
and glycerol optionally together with bifunctional alcohols (for
example, aliphatic glycols such as ethylene glycol, diethylene
glycol, 1,2-propanediol, and neopentyl glycol) and a small amount
of tetrafunctional alcohols (for example, pentaerythritol).
As polyester B, those obtained from the following carboxylic acid
components and alcohol components may be preferably employed.
Carboxylic Acid Component
Materials comprising terephthalic acid and/or isophthalic acid
optionally together with other polyvalent carboxylic acids such as
aromatic dicarboxylic acids (for example,
2,6-naphthalenedicarboxylic acid), a small amount of tri- or higher
valent aromatic carboxylic acids (for example, trimellitic acid,
pyromellitic acid), aliphatic dicarboxylic acids (for example,
succinic acid, adipic acid, azelaic acid) and alicyclic
dicarboxylic acids (for example, 1,4-cyclohexanedicarboxylic
acid).
Alcohol Component
Materials comprising ethylene glycol and neopentyl glycol
optionally together with aliphatic glycols (for example, diethylene
glycol, 1,2-propanediol) and a small amount of tri- or higher
valent alcohols (for example, trimethylolpropane,
pentaerythritol).
The average degrees of polymerization of polyesters A and B may
preferably be from 4 to 50, since such a polyester can be easily
powdered.
Furthermore, the softening points of polyesters A and B may
preferably be from 50 to 150.degree. C. When the softening point of
a polyester is lower than 50.degree. C., the powdered resin is
liable to be solidified through aggregation, and thus the blocking
resistance of the coating is deteriorated. When the softening point
exceeds 150.degree. C., on the other hand, it is necessary to
employ an elevated kneading temperature. As a result, the reaction
of the resin composition with the hardener would proceed during the
formulation of the coating, and therefore the smoothness and
mechanical strength of the obtained coating film are
deteriorated.
The resin composition for a powder coating according to the present
invention may be produced by kneading the above-mentioned
polyesters A and B and the hardener by using a kneader or a roller
at a temperature of from 70.degree. to 150.degree. C.
The resin composition of the present invention may further contain
other additives (for example, leveling agents, hardening
catalysts), if required .
To further illustrate the present invention in greater detail, the
following Examples and Comparative Examples will be given.
The characteristic data were determined by the following
methods.
Average Degree of Polymerization
Determined by gel permeation chromatography.
Hydroxyl Value
Determined by the above-mentioned method.
Acid Value
Determined by dissolving a sample in dioxane and then titrating
with a solution of potassium hydroxide in methanol.
Softening Point
Determined by heating a sample on a hot bench and then observing
with the naked eye.
Gel Time
Determined by the above-mentioned method.
Specular Gloss at 60.degree.
Determined in accordance with JIS K 5400.
Impact Resistance
In accordance with JIS K 5400, determined by using a ball
(diameter: 1/2in., weight: 500 g).
Weight Loss
The ratio of the difference in weight before and after the
hardening reaction to the weight before the reaction was
determined.
REFERENCE EXAMPLE 1
Preparation of Polyester A
The compounds as specified in Table 1 were introduced into a
stainless reaction vessel provided with stirring blades and heated
to 230.degree. C. under stirring. The water thus formed was
continuously removed from the reaction system. After keeping the
reaction mixture under the reduced pressure of 600 mmHg for 3
hours, the compound as specified in Table 2 was added thereto. The
mixture was stirred in a closed system for 1 hour to thereby obtain
a polyester resin 1.
REFERENCE EXAMPLE 2
Preparation of Polyester A
The compounds as specified in Table 1 were introduced into a
stainless reaction vessel provided with stirring blades and heated
to 230.degree. C. under stirring. The water thus formed was
continuously removed from the reaction system. After keeping the
reaction mixture under the reduced pressure of 600 mmHg for 3
hours, a polyester resin 2 was obtained.
REFERENCE EXAMPLE 3-5
Preparation of Polyester B
The compounds as specified in Table 1 were introduced into a
stainless reaction vessel provided with stirring blades and heated
to 260.degree. C. under stirring. The water thus formed was
continuously removed from the reaction system. Next, 5.84 parts by
weight of antimony trioxide were added thereto as a
polycondensation catalyst. Then the obtained mixture was subjected
to a polycondensation reaction at 280.degree. C. for 2 hours under
reduced pressure of 1.0 to 0.5 mmHg or below to thereby obtain a
polyester resin having a high degree of polymerization. After
cooling to 270.degree. C., the compound as specified in Table 2 was
added to the obtained resin. After depolymerizing in a closed
system, polyester resins 3 to 5 were obtained.
Table 3 shows the characteristic data of each polyester resin.
TABLE 1 ______________________________________ Reference Example 1
2 3 4 5 ______________________________________ terephthalic 3320
16600 16600 16600 acid isophthalic 13280 17000 acid ethylene 3100
3720 5890 glycol neopentyl 520 11440 10400 6760 glycol bisphenol S
3380 ethylene oxide trimethylol- 15810 15410 propane (parts by
weight) ______________________________________
TABLE 2 ______________________________________ Reference Example 1
3 4 5 ______________________________________ isophthalic 230 acid
neopentyl 100 glycol trimethylol- 540 670 540 propane (parts by
weight) ______________________________________
TABLE 3 ______________________________________ Polyester 1 2 3 4 5
______________________________________ average degree 4.6 5.2 25.3
16.2 25.5 of polymerization hydroxyl value 4810 4370 500 730 540 (g
eq/10.sup.6 g) acid value 64 43 9 10 10 (g eq/10.sup.6 g) softening
point 70 78 89 80 85 (.degree.C.) gel time (min.) 4.1 4.2 12.0 9.5
8.4 (4.4) (4.4) (12.8) (10.2)
______________________________________ Data given in parentheses
are obtained by using a hardener B 1530.
EXAMPLES 1 TO 4 AND COMPARATIVE EXAMPLES 1 to 4
Each polyester resin as specified in Table 4, a hardener (IPDI-BF
1540 manufactured by Huls Co.; inner blocked isocyanate or B 1530
manufactured by Huls Co.: .epsilon.-caprolactam blocked
isocyanate), a leveling agent (Acronal 4F manufactured by BASF
Co.), benzoin, a hardening catalyst (Stann OMF manufactured by
Sankyo Yuki Gosei K.K.), an epoxy resin (Epo Tohto YD 014
manufactured by Tohto Kasei K.K.), titanium dioxide and
precipitated barium sulfate were dry-blended at the ratio as
specified in Table 4 in a Henschel mixer (FM 10B manufactured by
Mitsui Miike Seisakusho K.K.) and then kneaded in a molten state in
a Ko-kneader (PR-46 manufactured by Buss Co.) at a temperature of
90 to 110.degree. C. After cooling and grinding, the product was
passed through a wire mesh (140 mesh) to thereby obtain a powder
coating.
The powder coating thus obtained was electrostatically applied onto
a steel plate treated with zinc phosphate in such a manner as to
provide a film thickness of 50 to 60 .mu.m followed by baking at
200.degree. C. for 20 minutes.
Table 5 shows the results of the evaluation of the film
properties.
TABLE 4 ______________________________________ Comparative Example
Example 1 2 3 4 1 2 3 4 ______________________________________
polyester resin 1 24 26 24 polyester resin 2 15 20 15 40 polyester
resin 3 54 31 54 10 polyester resin 4 36 36 42 polyester resin 5 48
42 hardener BF 1540 31 32 40 43 50 16 hardener B 1530 31 40
leveling agent 1 1 1 1 1 1 1 1 benzoin 0.5 0.5 0.5 0.5 0.5 0.5 0.5
0.5 hardening catalyst 0.3 0.3 epoxy resin 2 2 titanium dioxide 50
50 35 50 50 35 50 50 barium sulfate 15 15 (parts by weight)
______________________________________
TABLE 5 ______________________________________ Example Comparative
Example 1 2 3 4 1 2 3 4 ______________________________________
difference in 7.8 4.2 5.4 7.9 8.4 5.8 7.8 1.1 gel time (min.)
specular gloss 9.5 40.3 57.5 38.8 4.1 28.3 83.3 88.1 at 60.degree.
(%) impact resis- >50 40 40 >50 40 >50 20 >50 tance
(cm) weight loss 1.2 1.5 1.4 1.6 14.6 18.5 2.1 1.6 (%)
______________________________________
According to the present invention, a resin composition for a
powder coating capable of providing a stable mat or semimat coating
film which is excellent in mechanical strength which is accompanied
by no vaporization of a blocking agent with a small weight loss
during the reaction can be obtained.
While the invention has been described in detail and with reference
to specific embodiments thereof, it will be apparent to one skilled
in the art that various changes and modifications can be made
therein without departing from the spirit and scope thereof.
* * * * *